Raymond r



Aug. 7,1928. 1 4 1,680,272

R. R. MACHLETT LIUMINOUS'TUBE AND PROCESS OF muumc'runme THE SAME FiledNov. 17, 1927 IN VENTOR ia. M m

I in con unction Patented Aug. 7, 1928.

UNITED STATES PATENT OFFICE.

RAYMOND R. NIACHLETT OF NEW YORK, N. Y., ASSIGNOR TO RAINBOW LIGHT, INQ,OF

LONG ISLAND CITY, NEW YORK, A CORPORATION OF NEW YORK.

LUMINOUS TUBE AND PROCESS OF MANUFACTURING THE SAME.

Application filed November 17, 1927. Serial N0. 233,772.

My present invention relates to an improved luminous discharge tube andto an improved process of manufacturing the same. The improved tube isof the type in which interior electrodes are used and which contains ararefied atmosphere comprising .an inert gas, such as neon. Argon,helium or other so-callcd noble gas may be used either alone or incombination, and mercury vapor in minute quantity may be employedtherewith in order to increase the range' of colors.

' The pressure of will become luminous under the effect of an"electrical discharge. Vith neon, for example, although the pressure atwhich maximum conduction occurs is in the neighborhood of l m. m'. ofmercury. absolute, yet initial pressures in the neighborhood of 8 to 10iii. In. are preferred, since in this way the life of the tube may beenormously increased without necessitating the employment ofprohibitively long tubes.

\Vith my improved possible to employ electrodes which are of cry smallsize, and hence can be more cheaply manufactured and installed. Thesesmall electrodes also enable the tube to be made with end portions whichare not unduly large and cumbersome. This feature of the invention isparticularly valuable in connection with tubes of large size, such as aneon beacon, in which very heavy currents are employed.

When ordinary interior electrodes are used it is important that thecurrent density should be such as not to increase the normal cathodedrop of potential, and this means that the negative glow should notextend further than to just encompass the electrode surface. If thecurrent density is increased beyond this normal value, a very great risein the cathode drop takes place accompanied by heating, and thephenomenon of sputtering or vaporization becomes much more pronouncedwith an accompanying depletion of the conducting atmosphere, a reductionin the pressure, and eventually in the failure of the tube to conduct.The life of the tube is thus shortened.

I have found that with ordinary interior electrodes the critical area atwhich the normal cathode drop tends to become abnormal is between 10 and1.4 sq. deeimeters per amthe gas is such that it luminous tube it ispereof current with neon gas at a pressure of 7 in. m. of mercury. As thepressure of gas is diminished the cr tical electrode area becomes largerand, therefore, it is the practice to make'the electrodes substantiallylarger than the critical value at the pressure of gas employed, in orderthat,'as the pressure is reduced. the normal cathode drop may still hemaintained. It would not be commercially practicable to make theelectrodes sufliciently large to maintain the normality of the cathodedrop with the gas at the minimum pressure when conduction has ceased,because to do that would involve the use of electrodes of enormous size.

Commercial practice, therefore, is in the nature of a compromise,theelectrodes being substantially larger than the critical area referredto, in order to take care of a substantial reduction of pressurerepresenting the greater part of the life of the tube Then, as thepressure tends to still further decrease, there will be a gradualincrease in the cathode drop representing further useful life. The finalhours of the tube Will be those in which the sputtering becomes veryviolent, since this phenomenon is greatest at low pressures.

By means of my invention I am enabled to make a luminous tube in whichthe electrode area is many times smaller than that required by theclass' :al rules of current density, so that a neon beacon, for example,can be made and operated with currents of from 5 to 10 amperes or moreand yet the electrodes will be of relatively small size. This is anextremely important consideration in the commercial manufacture of verylarge luminous tubes where the employment of ordinary interiorelectrodes might involve the use of glass chambers several feet long anda foot or more in diameter.

The method which I have developed for making these tubes is a specificimprovement on the process disclosed in my Patent, No.- .1.618,767,dated February 22, 1927. With the patented process I am enabled toobtain a luminous tube in its complete final state of puritymlirectlyfrom the pumping apparatus and without the necessity of further aging orseasoning, thereby securing a substantial saving of time of manufacture.\Vith my present method I employ the same fundamental idea disclosed insaid patent,

, a great saving of time will be effected.

\Vhile the improved process is especially intended for use in themanufacture ofluminous tubes having interior electrodes and finds itsgreatest value in this field, yet it may be employed in the manufactureof tubes having exterior electrodes.

My objects generally are to provide an im )rovcd luminous tube of highefiiciency and long life and employing electrodes of relatively smallsize and to provide a process by which such tubes may be economicallymanufactured, all, as 1 will hereafter described and claim.

In order that the invention may be better understood attention isdirected to the accompanying drawing, in which Figure 1 is a perpesctiveview of a suitable oven for processing the tubes, showing three tubestherein, the front of the oven being elevated to disclose its interior;and

Figure 2 a side elevation. on a somewhat larger scale, showing a singletube in process of manufacture.

In both of these views corresponding parts are represented by the samenumerals.

1 represents the improved luminous tube which is shown as having astraight central portion and enlarged ends 2-2, made'preferably ofboro-silica glass having a high melting point, as disclosed in saidpatent. It will be understood, of course, that the shape of the tube isunimportant.

The enlarged chambers 2-2 of the tube are formed with inwardly-extendingnecks 3, in which are sealed the conductors 44 leading to the electrodes5-5. Each electrode is supported upon a neck or tube 6 made prefcrablyofquartz.

The electrodes 55 are made of a conducting material having the propertyof occluding or absorbing substantial amounts of 'the alkali vaporadmitted to the tube, as I will hereafter describe. I have found thatgraphite or other forms of carbon are admirably suited for the purpose.

The surface area of the electrodes is rela-' tively small, and I have inpractice made use of. graphite electrodes having a surface area as lowas .6 decimeters per ampere of current with neon gas at a pressure of 7.

m. m. of mercury. Electrodes of this size give excellent results andremain cool in operation, at least for most of the life of the tube,which may be several thousand hours. In processing the improved tubes anumber of them are mounted side by side and secured together bytubulations 7 leading to a common tube 8 and supported by .hangers 9within a suitable oven 10. For the purpose of illustration I show threeof these tubes 1 in the oven 10, although the number may be 'more orless. By thus simultaneously processing a plurality of tubes, I verygreatly extend the capacity of the ovens and reduce the time required toperform the necessary operations. \Vith the method disclosedspecifically in my patent above referred to, one tube at a time isprocessed and the operationfurther involved the carrying out of thesteps which I am now able to dispense with, as I will describe.

The oven 10 is heated in any suitable way, such as by means of gas jets11 located below a perforated partition 12. It is also provided with adoor 13 capable of being lifted up and down or otherwise opened andclosed, and said door is provided with one or more sight openings 14therein covered with mica, in order to permit the tubes within the ovento be observed.

A tubulation 15 depends from each tube preferably near its centre andcontains a small quantity 16 of an alkali metal, the vapor of which isto be employed as the purging agent.

The tube 18 extends through one of the I side walls of the oven. andleads to suitable pumping apparatus as indicated. This may be of anysuitable and approved type. In my patent I have indicated morespecifically a desirable arrangement.

The tube .8 is also provided with *a branch tube 15 leading to asuitable gas supply, such as neon. Valves 16and' to cut oil the tubeswhich are being processed from the pumping apparatus or gas supply asmay be needed.

The conductors 4 are shown in Figure 2 as being connected to thesecondary 18 of a transformer, the primary 19 of which is in circuitwith a suitable source of alternab ing current 20. All of the tubes havesimilar electrical connections and their conductors 4 may be connectedin multiple with, a single secondary 18, as will be obvious.

Assuming that the tubes are supported within the oven. as shown inFigure 1 and that the" door 13 is closed, the process is carried out asfollows:

The pumping apparatus being started, air will be exhaustedsimultaneously from all the tubes. Vhen the pressure has beensufficiently reduced all the electrodes in the tubes are strongly heatedby the passage of a heavy current through the same. The ef-- fect ofthus heating the electrodes is to drive off gases occluded therein andto activate the carbon ofwhich they are composed, so as to make itstrongly susceptible to the occlusion of the alkali metal vapor whenthis is provided. The current which is employed for thus activatingthe'electrodes is substantially greater than the normal value of thecurrent with which the tube is 17 are shown. 1

metal '16 ives. 11 tubes; The tern nature to which the aesegm pends eeaae m lill to 1): ttiv l em a at ee s a [invariant Pa te Sti e ape a 1aePQa-a a or h as been thhs through the tubes the heating is dis'cbii'.lfiued and the' tgnbeszarre a-lloyfir fiqfi The pas sage ot the cufrntis also discontinued. As soon as the oven temperature has droppedsufficiently low, the several tubulations 15 are sealed'ofi so as toarrest the supply of alkali metal vapor and the pumping continuesthereafter until substantially all traces of the vapor have beendI'HWILOfi from the tubes, Any residual vapor remaining in the tubeswill be too slight to have any efi'ect on the color or electricalcharacteristics of the tube.

The valve 16 is now closed to cut oil the pump and the valve 17 isopened to permit the introduction into all the tubes of neon or otherrare gas at the desired pressure,

'ious 1m purities ab lbentv e a Jpe a are. l-lL ther in automatically,

, mer hea, in wthe-utube 2. An improved luminous tube, comprising atransparent tubular container-having therein a rare gas of theatmosphere under reduced pressure, and interior electrodes within thetube of carbon having an alkali metal vapor occluded therein,"substantially as set forth.

3. An improved luminous tube, comprising a transparent tubular containerhaving therein a rare gas of the atmosphere under reduced pressure, andinterior electrodes within the tube of graphite having an alkali inga.

reduced ,pressure, .within the tube of vapor occluded therein, substantiy as set occluded therein, substantially forth. 5. An improved luminoustube, comprismg a transparent tubular container havingneon therein underreduced pressure, and mterior electrodes within the tube of carbonhaving an alkali metal vapor occluded therein, substantially as setforth.

6. An improved luminous tube, compristransparent tubular containerhaving neon therein under reduced pressure, and interior electrodeswithin the tube of carbon vmg carsium vapor occluded therein,substantially as set forth- 7. An improved luminous tube, comprising atransparent tubular container having therem a rare gas of the atmosphereunder reduced presure, and interior electrodes w thin the tube of carbonhaving an alkali metalvapor occluded therein, the area of each of saidelectrodes being less than one square decimeter per ampere of normalcuring a transparent neon therein under reduced a tubular rent at a gaspressure of 7 A; m. m. of mer cury, substantiall as set forth.

8. An lmprov luminous tube, compristubular container having pressure,and interior electrodes within the tube of carbon having an alkali metalvapor occluded therein, the area of each of said electrodes being 1cmthan one square decimeter per ampere of normal current at a gaspressu'reof 7 in. m. of mercury, substantially as set forth.

9. An improved luminous tube, compriscontainer having neon therein underreduced pressure, and interior electrodes within the tube of carbonhaving caasium-va r occluded therein, the area ofeach of said electrodesbeing less than one square decimeter per ampere of normal current at agas pressure of 7% m. m. of mercury, substantially as set forth.

10. The method of processing luminous forth.

11. The method of processing luminous tu having interior carbonelectrodes and provided with a tubulation containing caesium, whichconsists in passing a heavy rent between the electrodes to activatethem, in creating a partial vacuum within the tube and tubulation, insubjecting both the tube and tubulation to a heated atmosphere, wherebyunder the reduced pressure caesium vapors will be evolved and will bediffused through the tube and become occluded in the electrodes, and inpassing a current of substantially normal value between the electrodesbefore sealing off the tubulation until under the spectroscope thespectrum of caesium. is alone visible, substantially as set forth.

12. The method of processing" luminous tu containing interior electrodesof carbon and provided with a tabulation containing caesium, whichconsists in creating a partial vacuum Within the tube and tubulation, inthen activating the electrodes-in then subjecting the tube andtabulation to the eflect of heat, whereby under thereduced pressurecaesium vapor will be evolved and will be difi'used through the tube soas to be occluded in the electrodes, in maintaining a current ofsubstantially normal value within the tube, before sealing oil thetubulation, said current being maintained until the pure caesiumspectrum is alone visible, in then redu the temperature of the tube andcontinuing the exhaustion so as to remove substantially all of the freevapor within the tube and in finally admitting the desired rare gaswithinthe .tube, substantially as set forth.

RAYMoNn R. MACH'LETT.

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